THE JOURNAL OF NOAMI, VOL 28, NUMBER-1, JUNE 2011, Jun 10, 2011
The coast line of Bangladesh has always been undergoing through several changing phases caused by... more The coast line of Bangladesh has always been undergoing through several changing phases caused by radical accretion and erosion of lands along the coastal zone. Huge sediment supply by the Ganges-Brahmaputra-Meghna river system contributes significantly for land accretion whereas combined effect of natural calamities and anthropogenic activities causes considerable erosion, especially along the western deltaic coast and eastern cliff coast of Bangladesh. The present approach is taken to give an overview of land changes in Bangladesh coast through GIS analysis using multi temporal satellite imageries since 1972 to present with a view to quantify and qualify the changes of coastal area caused by land accretion and erosion in short (5-6 years) and long (10-16 years) time period.
From short and long time interval analysis reveals that the entire coast of Bangladesh exhibits a mixing trend of land accretion and erosion. The analysis also pointed out some exceptional episodes regarding the land configuration in few portions of the coastal zone. Sunderbans, the largest mangrove forest, experienced largest area of land loss during 1989-1999 which was about 67 sqkm. Subsequent gaining phase initiated in 2005 and was terminated in 2010. The landmass of Meghna Estuary and eastern part of Lower Ganges Delta has always been in gaining phase with one exception during 1989 to 1999 that lost 81 sqkm of land. Overall accretion in this particular area is about 769 sqkm. During the time span 1977-2010 Sandwip and Kutubdia islands are prone to erosion. Sandwip Island is discovered to experience only one gaining phase, adding 11.7 sqkm during the time period 1989-2001.Whereas Kutubdia Island exhibits accretionary phase during 1999-2005 contributing only 2.6 sqkm. Present study reveals that about 57 sq. km area of Sandwip and 9 sqkm area of Kutubdia islands are being eroded since 1972 to 2010. In contrast, rate of accretion exceeds the rate of erosion in Moheshkhali Island. More than 39.3 sqkm area accreted over thirty eight years. The Chittagong coast is almost in steady state. Approximately 46.1 sqkm area is added since 1978. Cox’s Bazar-Teknaf coast can be characterized by slight loosing phase. During 1972-2010, about 21.70 sq. km area of this coast is eroded.
The overall scenario affirm by the composite image analysis over thirty years shows that the Sundarbans and Lower Ganges deltaic coast is in slightly erosional phase, the Meghna Estuary is in gaining phase and mix trend characterizes the cliff coast. The coast of Sundarbans and northern part of cliff coast are more or less in steady condition, on the other hand Kuakata of deltaic coast, east of Bhola, north of Hatia and Sandwip island, Kutubdia Island, Kalatali beach, Shahpurirdwip and Badarmakam of the cliff coast that suffer from severe erosion. Devastating action of major cyclones, storm surges, longshore current, strong tidal action, local wave action and of course anthropogenic activities are the most probable causes of land erosion. The temporal erotic changes with overall tendency might be related with short-term episodic phenomena.
Bookmarks Related papers MentionsView impact
Uploads
Keywords CVI . Bhola island . Sea level change. Geospatial techniques
of southern low-lying peat deposits in Madaripur and part of Gopalganj district that covers approximately 17,000 hectare areas. Based on the survey of 800 boreholes, drilled in this region at different times by several government and non-government organizations for the purposes of peat exploration and hydrogeological investigation, reveals that the study area is composed of a considerable amount of peat deposits in various localities among which the deposits at Baghia-Chanda beel in Madaripur and Gopalganj districts are the most remarkable. The average peat thickness (in-situ condition), studied during field investigation, is 6.5 feet for the upper peat deposits, overlying with an average of 3.5 feet of alluvium cover, followed by the lower peat layer of about 3 feet thick that begins at an average depth of 8 feet and separated by a thin bluish grey silty clay sediments from the upper one. The lower part of the study area, locally known as beels, is the most prospective region for peat, whereas the western part is less potential either having no peat intersection or minimal peat thickness. The overburden covers, on the other hand are inversely correlated with the peat thicknesses, i.e., thick overburden tend to correlate with thin peat deposits and the thickest peat intersections have no or minimal overburden. Due to the variation in bulk density and peat depth, this Holocene peat has an average of 59.10% carbon stock. Nitrogen levels, more than 3%, indicate that the peat developed from the decomposition of reeds, sedges,bushes and trunks of trees (higher in nitrogen) rather than either moss or grass (lower in nitrogen). Higher sulphur content (about 2.7%) reflected the influence of brackish environments where the formation of FeS2 took place in the roots of existing vegetation. The calorific values, about 1308.8 k-cal/kg (after 20% moisture reduction), suggest that the Gopalganj-Madaripur peat is a low grade fuel that can be used as an alternative energy source in the domestic and limited industrial purposes , to relatively expensive natural gas and coal.
"
Sedimentary sequences of the northern and north eastern fringe of Moheshkhali coastal plain and northern part of Kutubdia Island exhibit similar characters with those of the Matamohuri estuarine plain which was occupied and protected by the Chakoria Sundarbans in recent past. The present geomorphological context together with thick and repetitive sequences of fine and peaty sediments alternating with sands containing shell fragments and wood debris are indicative to an estuarine environment of a protected depositional system for eastern part of Moheshkhali coastal plain and northern part of Kutubdia Island. On the other hand, sediments of the southern and western fringe of Moheshkhali coastal plain, Sonadia, Matarbari and southern part of Kutubdia islands seem to be an open to semi-protected depositional system. The present shore-faces of these areas are characterized by the presence of numerous long-shore bars along the west coast of Kutubdia and Sonadia and barriers are found to occur from the southwestern edge of Matarbari to the northern tip of Sonadia islands, and along the western margin of the Moheshkhali coastal plain. The presence of remnants of beach rock sequence at the lowest low-water level at south-west of Baraghop, Kutubdia Island and Oyster reef at mid-west shore of Matarbari Island also establish the open basin depositional system.
"
From short and long time interval analysis reveals that the entire coast of Bangladesh exhibits a mixing trend of land accretion and erosion. The analysis also pointed out some exceptional episodes regarding the land configuration in few portions of the coastal zone. Sunderbans, the largest mangrove forest, experienced largest area of land loss during 1989-1999 which was about 67 sqkm. Subsequent gaining phase initiated in 2005 and was terminated in 2010. The landmass of Meghna Estuary and eastern part of Lower Ganges Delta has always been in gaining phase with one exception during 1989 to 1999 that lost 81 sqkm of land. Overall accretion in this particular area is about 769 sqkm. During the time span 1977-2010 Sandwip and Kutubdia islands are prone to erosion. Sandwip Island is discovered to experience only one gaining phase, adding 11.7 sqkm during the time period 1989-2001.Whereas Kutubdia Island exhibits accretionary phase during 1999-2005 contributing only 2.6 sqkm. Present study reveals that about 57 sq. km area of Sandwip and 9 sqkm area of Kutubdia islands are being eroded since 1972 to 2010. In contrast, rate of accretion exceeds the rate of erosion in Moheshkhali Island. More than 39.3 sqkm area accreted over thirty eight years. The Chittagong coast is almost in steady state. Approximately 46.1 sqkm area is added since 1978. Cox’s Bazar-Teknaf coast can be characterized by slight loosing phase. During 1972-2010, about 21.70 sq. km area of this coast is eroded.
The overall scenario affirm by the composite image analysis over thirty years shows that the Sundarbans and Lower Ganges deltaic coast is in slightly erosional phase, the Meghna Estuary is in gaining phase and mix trend characterizes the cliff coast. The coast of Sundarbans and northern part of cliff coast are more or less in steady condition, on the other hand Kuakata of deltaic coast, east of Bhola, north of Hatia and Sandwip island, Kutubdia Island, Kalatali beach, Shahpurirdwip and Badarmakam of the cliff coast that suffer from severe erosion. Devastating action of major cyclones, storm surges, longshore current, strong tidal action, local wave action and of course anthropogenic activities are the most probable causes of land erosion. The temporal erotic changes with overall tendency might be related with short-term episodic phenomena.
The Meghna and the Tetulia are the major rivers of the investigated area both of which are influenced by fluvial and tidal processes. In addition to these, a network of interconnected innumerable tidal channels, creeks and inlets have formed drainage system of the mapped area.
Bhola is not a solitary island. It is a complex land mass formed by combination of isolated estuarine mouth bars through fluvo-tidal processes. On the basis of its origin Bhola Island can be divided into three different units such as 1) Northern Unit, 2) Central Unit and 3) Southern Unit and newly born chars depending on their aerial extent, elevation difference, soil characteristics, Palaeosol, geology, sedimentology, vegetation, channel characters and vertical log data. Vertical sequence of Northern unit shows two repeated bar cycles which reflect appearance of same depositional environment.
A geomorphic approach has been followed to divide the terrain of the area into well-defined physically identifiable and genetically significant units. The geomorphic units with their distinct characteristic deposits constitute the geological units of the area. The Holocene sediment covering the mapped area can be divided into 5 distinct map units. The units are: (1) Bar Deposits (2) Tidal Flood Plain Deposits (3) Protected Supratidal Flat Deposits (4) Supratidal Flat Deposits and (5) Intertidal Flat Deposits. The sediments of the area consists mainly admixture of clay, silt and fine sand.
"
Keywords CVI . Bhola island . Sea level change. Geospatial techniques
of southern low-lying peat deposits in Madaripur and part of Gopalganj district that covers approximately 17,000 hectare areas. Based on the survey of 800 boreholes, drilled in this region at different times by several government and non-government organizations for the purposes of peat exploration and hydrogeological investigation, reveals that the study area is composed of a considerable amount of peat deposits in various localities among which the deposits at Baghia-Chanda beel in Madaripur and Gopalganj districts are the most remarkable. The average peat thickness (in-situ condition), studied during field investigation, is 6.5 feet for the upper peat deposits, overlying with an average of 3.5 feet of alluvium cover, followed by the lower peat layer of about 3 feet thick that begins at an average depth of 8 feet and separated by a thin bluish grey silty clay sediments from the upper one. The lower part of the study area, locally known as beels, is the most prospective region for peat, whereas the western part is less potential either having no peat intersection or minimal peat thickness. The overburden covers, on the other hand are inversely correlated with the peat thicknesses, i.e., thick overburden tend to correlate with thin peat deposits and the thickest peat intersections have no or minimal overburden. Due to the variation in bulk density and peat depth, this Holocene peat has an average of 59.10% carbon stock. Nitrogen levels, more than 3%, indicate that the peat developed from the decomposition of reeds, sedges,bushes and trunks of trees (higher in nitrogen) rather than either moss or grass (lower in nitrogen). Higher sulphur content (about 2.7%) reflected the influence of brackish environments where the formation of FeS2 took place in the roots of existing vegetation. The calorific values, about 1308.8 k-cal/kg (after 20% moisture reduction), suggest that the Gopalganj-Madaripur peat is a low grade fuel that can be used as an alternative energy source in the domestic and limited industrial purposes , to relatively expensive natural gas and coal.
"
Sedimentary sequences of the northern and north eastern fringe of Moheshkhali coastal plain and northern part of Kutubdia Island exhibit similar characters with those of the Matamohuri estuarine plain which was occupied and protected by the Chakoria Sundarbans in recent past. The present geomorphological context together with thick and repetitive sequences of fine and peaty sediments alternating with sands containing shell fragments and wood debris are indicative to an estuarine environment of a protected depositional system for eastern part of Moheshkhali coastal plain and northern part of Kutubdia Island. On the other hand, sediments of the southern and western fringe of Moheshkhali coastal plain, Sonadia, Matarbari and southern part of Kutubdia islands seem to be an open to semi-protected depositional system. The present shore-faces of these areas are characterized by the presence of numerous long-shore bars along the west coast of Kutubdia and Sonadia and barriers are found to occur from the southwestern edge of Matarbari to the northern tip of Sonadia islands, and along the western margin of the Moheshkhali coastal plain. The presence of remnants of beach rock sequence at the lowest low-water level at south-west of Baraghop, Kutubdia Island and Oyster reef at mid-west shore of Matarbari Island also establish the open basin depositional system.
"
From short and long time interval analysis reveals that the entire coast of Bangladesh exhibits a mixing trend of land accretion and erosion. The analysis also pointed out some exceptional episodes regarding the land configuration in few portions of the coastal zone. Sunderbans, the largest mangrove forest, experienced largest area of land loss during 1989-1999 which was about 67 sqkm. Subsequent gaining phase initiated in 2005 and was terminated in 2010. The landmass of Meghna Estuary and eastern part of Lower Ganges Delta has always been in gaining phase with one exception during 1989 to 1999 that lost 81 sqkm of land. Overall accretion in this particular area is about 769 sqkm. During the time span 1977-2010 Sandwip and Kutubdia islands are prone to erosion. Sandwip Island is discovered to experience only one gaining phase, adding 11.7 sqkm during the time period 1989-2001.Whereas Kutubdia Island exhibits accretionary phase during 1999-2005 contributing only 2.6 sqkm. Present study reveals that about 57 sq. km area of Sandwip and 9 sqkm area of Kutubdia islands are being eroded since 1972 to 2010. In contrast, rate of accretion exceeds the rate of erosion in Moheshkhali Island. More than 39.3 sqkm area accreted over thirty eight years. The Chittagong coast is almost in steady state. Approximately 46.1 sqkm area is added since 1978. Cox’s Bazar-Teknaf coast can be characterized by slight loosing phase. During 1972-2010, about 21.70 sq. km area of this coast is eroded.
The overall scenario affirm by the composite image analysis over thirty years shows that the Sundarbans and Lower Ganges deltaic coast is in slightly erosional phase, the Meghna Estuary is in gaining phase and mix trend characterizes the cliff coast. The coast of Sundarbans and northern part of cliff coast are more or less in steady condition, on the other hand Kuakata of deltaic coast, east of Bhola, north of Hatia and Sandwip island, Kutubdia Island, Kalatali beach, Shahpurirdwip and Badarmakam of the cliff coast that suffer from severe erosion. Devastating action of major cyclones, storm surges, longshore current, strong tidal action, local wave action and of course anthropogenic activities are the most probable causes of land erosion. The temporal erotic changes with overall tendency might be related with short-term episodic phenomena.
The Meghna and the Tetulia are the major rivers of the investigated area both of which are influenced by fluvial and tidal processes. In addition to these, a network of interconnected innumerable tidal channels, creeks and inlets have formed drainage system of the mapped area.
Bhola is not a solitary island. It is a complex land mass formed by combination of isolated estuarine mouth bars through fluvo-tidal processes. On the basis of its origin Bhola Island can be divided into three different units such as 1) Northern Unit, 2) Central Unit and 3) Southern Unit and newly born chars depending on their aerial extent, elevation difference, soil characteristics, Palaeosol, geology, sedimentology, vegetation, channel characters and vertical log data. Vertical sequence of Northern unit shows two repeated bar cycles which reflect appearance of same depositional environment.
A geomorphic approach has been followed to divide the terrain of the area into well-defined physically identifiable and genetically significant units. The geomorphic units with their distinct characteristic deposits constitute the geological units of the area. The Holocene sediment covering the mapped area can be divided into 5 distinct map units. The units are: (1) Bar Deposits (2) Tidal Flood Plain Deposits (3) Protected Supratidal Flat Deposits (4) Supratidal Flat Deposits and (5) Intertidal Flat Deposits. The sediments of the area consists mainly admixture of clay, silt and fine sand.
"